^aBayerisches Geoinstitut, Universität Bayreuth 95440 Bayreuth, Germany

^bInstitute of Mineralogy, Petrology and Economic Geology, Tohoku University, Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan

^cIstituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 00143 Roma, Italy

^dJapan Synchrotron Radiation Research Institute, 679-5198 Hyogo, Japan

Experiments have been performed between 2.8 and 13 GPa at temperatures ranging from 2043 to 2523 K. Measured viscosities range from 0.019 (± 0.004) to 0.13 (± 0.02) Pa s. At constant temperature, viscosity increases with increasing pressure up to  8.5 GPa but then decreases between  8.5 and 13 GPa. The change in the pressure dependence of viscosity is likely associated with structural changes of the liquid that occur upon compression. By combining our results with recently published 0.1 MPa peridotite liquid viscosities D.B. Dingwell, C. Courtial, D. Giordano, A. Nichols, Viscosity of peridotite liquid, Earth Planet. Sci. Lett. 226 (2004) 127–138.], the experimental data can be described by a non-Arrhenian, empirical Vogel-Fulcher-Tamman equation, which has been modified by adding a term to account for the observed pressure dependence of viscosity. This equation reproduces measured viscosities to within 0.08 log₁₀-units on average. We use this model to calculate viscosities of a peridotitic magma ocean along a liquid adiabat to a depth of  400 km and discuss possible effects on viscosity at greater pressures and temperatures than experimentally investigated.